Splitting a mesh at the end of a shape key-based animation
Consider switching from 1 mesh to 2 meshes if convenient.  Render or Not Render is animatable with keyframes.  Combined Mesh is replaced with Floor Mesh and Floating Bubble Mesh.  Advantage Seams are avoided. Disadvantage Shape Continuity efforts will be needed.
Consider your mesh as always 2 separate submeshes if the Viewer cannot see seam vertices which are joined for part of the animation.  Shrinkwrap Modifier and Warp Modifier.
Consider Metaballs with reservations.  Explained Below.
Consider fluid simulations.  Larger Compute Time Demands.


Two Separate Meshes
Preliminary Results.
Warp Modifiers. Shrink Wrap Modifier.  No Shape Keys Yet.







Metaballs

Lower Portion Connected in image below.


Lower Portion Disconnected in image below.




I wrote with reservations because I have seen metaballs stop working at the most inconvenient times and simple conditions.    Then they work under other conditions such as particles.